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Author Topic:   New helium retention work suggests young earth and accelerated decay
edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 61 of 107 (22616)
11-14-2002 12:15 AM
Reply to: Message 59 by edge
11-14-2002 12:14 AM


Double (triple!!?)posting deleted.
[This message has been edited by edge, 11-14-2002]

This message is a reply to:
 Message 59 by edge, posted 11-14-2002 12:14 AM edge has not replied

Minnemooseus
Member
Posts: 3941
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 10.0


Message 62 of 107 (22623)
11-14-2002 12:58 AM


From message 48:
quote:
One of the strongest pieces of evidence I know of for accelerated decay is the high retention of radiogenic 4He in microstopic zircons. Figure 5 summarizes the data [Gentry et al., 1982b]. These zircons, about 75 microns long, are embedded in crystals of biotite (black mica). In turn, the biotite is embedded in hot Precambrian basement granodiorite (granitic rock) below the Jemez volcanic caldera near Los Alamos, New Mexico. Radioisotopic (Pb-Pb) dating of zircons recovered from deep boreholes in the formation give an age of "1.5 billion years" [Zartman, 1979].
My bolds.
and
quote:
Diffusion rates of radiogenic He through bare zircons, not embedded in other crystals, have been measured, as Figure 6 shows [Magomedov, 1970]. Those rates are too fast to retain the He for more than a few decades even at room temperatures. However, the biotite crystals in which the Jemez zircons were embedded could "bottle up" the He in the zircons, causing longer retention times. So the real question is: how fast does He diffuse through biotite?
I am presuming that these difusion rates were measured at 1 atmosphere of pressure.
Now, all this discussion is much to messy and complicated for a meer Moose brain to follow, but I will ask the question:
Were presure considerations made, in studying the diffusion rates?
Apparently at least some of the zircon samples were taken from a considerable depth (and higher much higher than atmospheric presure).
Moose

Replies to this message:
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wehappyfew
Inactive Member


Message 63 of 107 (22650)
11-14-2002 7:42 AM
Reply to: Message 62 by Minnemooseus
11-14-2002 12:58 AM


Actually, moose, diffusivity experiments are done under vacuum. That's the way the experimental apparatus must operate. Presumably, what really matters is the partial pressure of helium. Even at great depths, this is still pretty low (but not zero).
Mathematically, I think it's possible to work out the diffusivity at ambient helium partial pressures other than zero, based on the experiments. There's some differential calculus involved, so don't ask me to do it. Here's a few equations to chew on:
Page not found - Canadian Society of Exploration Geophysicists
A change in helium partial pressure (from inside the zircon to the surrounding medium) results in a change in diffusivity that is more linear, while changing temp has an exponential effect on the diffusivity curve.

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Randy
Member (Idle past 6246 days)
Posts: 420
From: Cincinnati OH USA
Joined: 07-19-2002


Message 64 of 107 (22653)
11-14-2002 8:13 AM
Reply to: Message 63 by wehappyfew
11-14-2002 7:42 AM


quote:
Actually, moose, diffusivity experiments are done under vacuum. That's the way the experimental apparatus must operate. Presumably, what really matters is the partial pressure of helium. Even at great depths, this is still pretty low (but not zero).
I couldn't get the pdf file to open. I have done a little work on diffusion in some very different contexts but the same principles should apply. The driving force for diffusion is the difference in themodynamic activity, usually expressed as chemical potential of helium inside and outside the crytal. It seems to me that the chemical potential of helium outside the crystal will be essentially zero no matter what the pressure but I am not sure about the effect of pressure on thermodynamic activity in this case where behavior will be far from ideal. However, it also seems to me that the diffusion constant of helium inside the crystal may have a dependance on pressure. If helium diffuses by moving through "free volume" in the crystal and free volume is reduced when the crystal is under high pressure then the diffusion constant will presumably be reduced.
One caviat when extrapolating diffusion rates using activation energies is that the extrapolation is only valid if there is no phase change in the diffusion media. If the crystal undergoes any polymorphism it could be annealed at high temperature and then you could get a different down curve than up curve in a temperature study, which I think was seen. Of course I could be wrong about all of this because I have only studied diffusion in very different systems and that was some time ago.
Randy

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 Message 65 by edge, posted 11-14-2002 12:25 PM Randy has replied

edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 65 of 107 (22719)
11-14-2002 12:25 PM
Reply to: Message 64 by Randy
11-14-2002 8:13 AM


quote:
Originally posted by Randy:
...The driving force for diffusion is the difference in themodynamic activity, usually expressed as chemical potential of helium inside and outside the crytal. It seems to me that the chemical potential of helium outside the crystal will be essentially zero ...
Why would you think this?

This message is a reply to:
 Message 64 by Randy, posted 11-14-2002 8:13 AM Randy has replied

Replies to this message:
 Message 66 by Randy, posted 11-14-2002 1:07 PM edge has replied

Randy
Member (Idle past 6246 days)
Posts: 420
From: Cincinnati OH USA
Joined: 07-19-2002


Message 66 of 107 (22725)
11-14-2002 1:07 PM
Reply to: Message 65 by edge
11-14-2002 12:25 PM


quote:
Originally posted by edge:
quote:
Originally posted by Randy:
...The driving force for diffusion is the difference in themodynamic activity, usually expressed as chemical potential of helium inside and outside the crytal. It seems to me that the chemical potential of helium outside the crystal will be essentially zero ...
Why would you think this?

LIke I said I could be wrong. I was considering diffusion from crystal to the atmosphere. As think about it you have crystals that are in contact with other solid material that the He is diffusing into so they may have an appreciable concentration of He. Ultimately it is going somewhere and diffusion rates will be determined by the chemical potential and diffusion constant in each material it diffuses through. I have only ever worked with diffusion through membranes where things like partition coefficients also come into play and I don't know if there is anything equivalent in this situation. I think the main point I was trying to make is that diffusion constant may be pressure dependant if the crystal structure is affect by the pressures involved and it not necessarily legitmate to extrapolate over huge temperature ranges using activation energies because of the possiblity of physical changes in the crytal which could effect diffusion. I don't know if that really makes any sense with the crystals being discussed here but it seems that way to me.
Randy

This message is a reply to:
 Message 65 by edge, posted 11-14-2002 12:25 PM edge has replied

Replies to this message:
 Message 67 by edge, posted 11-14-2002 4:02 PM Randy has not replied

edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 67 of 107 (22755)
11-14-2002 4:02 PM
Reply to: Message 66 by Randy
11-14-2002 1:07 PM


quote:
Originally posted by Randy:
LIke I said I could be wrong. I was considering diffusion from crystal to the atmosphere. As think about it you have crystals that are in contact with other solid material that the He is diffusing into so they may have an appreciable concentration of He.
Which would change the rate of diffusion. I cannot support this, but I have heard that there is a steady flux of He through the crust.
quote:
Ultimately it is going somewhere and diffusion rates will be determined by the chemical potential and diffusion constant in each material it diffuses through. I have only ever worked with diffusion through membranes where things like partition coefficients also come into play and I don't know if there is anything equivalent in this situation. I think the main point I was trying to make is that diffusion constant may be pressure dependant if the crystal structure is affect by the pressures involved and it not necessarily legitmate to extrapolate over huge temperature ranges using activation energies because of the possiblity of physical changes in the crytal which could effect diffusion. I don't know if that really makes any sense with the crystals being discussed here but it seems that way to me.
I concur absolutely. The ability or inability to model actual, natural conditions has always bothered me.

This message is a reply to:
 Message 66 by Randy, posted 11-14-2002 1:07 PM Randy has not replied

Coragyps
Member (Idle past 734 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 68 of 107 (22792)
11-14-2002 7:26 PM


I'm not positive exactly how this factors in, but it's well established in the oilfield industry that pressure can have a very dramatic influence on "permeability" (approximately rate of diffusion) of gases in whole rocks. Measured perms in "tight gas sands" are frequently lower by a factor of 1000 at realistic native confining pressures than at atmospheric pressure. I would think that there should be some sort of analogy between this inter-grain permeability and the diffusivity along crystal defects that would control helium flow out of zircons. I'm not too sure I have the perseverance to look for documentation, though.

Replies to this message:
 Message 69 by wehappyfew, posted 11-14-2002 10:09 PM Coragyps has not replied

wehappyfew
Inactive Member


Message 69 of 107 (22806)
11-14-2002 10:09 PM
Reply to: Message 68 by Coragyps
11-14-2002 7:26 PM


quote:
Originally posted by Coragyps:
I'm not positive exactly how this factors in, but it's well established in the oilfield industry that pressure can have a very dramatic influence on "permeability" (approximately rate of diffusion) of gases in whole rocks. Measured perms in "tight gas sands" are frequently lower by a factor of 1000 at realistic native confining pressures than at atmospheric pressure. I would think that there should be some sort of analogy between this inter-grain permeability and the diffusivity along crystal defects that would control helium flow out of zircons. I'm not too sure I have the perseverance to look for documentation, though.
I agree. But I suspect that the effect is small enough at the shallow depths we are dealing with to safely ignored - at least for the relatively non-rigorous evaluation I am capable of. Any such effect would result in an overestimation of diffusivity from step-heating experiments conducted under vacuum. So this works in favor of Humphreys - my analysis will err in his favor.

This message is a reply to:
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TrueCreation
Inactive Member


Message 70 of 107 (22965)
11-16-2002 11:40 PM
Reply to: Message 60 by edge
11-14-2002 12:15 AM


"And yet, we see on another thread that TC has written:
"Catastrophic tectonics, flood surges, helium retention and a creationist cosmology IMO is the answer to your problems with YEC."
--Must've been another TC, whose the perpetrator?
------------------

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 Message 60 by edge, posted 11-14-2002 12:15 AM edge has replied

Replies to this message:
 Message 71 by edge, posted 11-16-2002 11:49 PM TrueCreation has not replied
 Message 73 by Tranquility Base, posted 11-17-2002 6:07 PM TrueCreation has not replied

edge
Member (Idle past 1705 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 71 of 107 (22968)
11-16-2002 11:49 PM
Reply to: Message 70 by TrueCreation
11-16-2002 11:40 PM


quote:
Originally posted by TrueCreation:
"And yet, we see on another thread that TC has written:
"Catastrophic tectonics, flood surges, helium retention and a creationist cosmology IMO is the answer to your problems with YEC."
--Must've been another TC, whose the perpetrator?
Could be. These strained assertions are so abundant that it is hard to keep them straight. I think it's a creationist conspiracy.

This message is a reply to:
 Message 70 by TrueCreation, posted 11-16-2002 11:40 PM TrueCreation has not replied

wehappyfew
Inactive Member


Message 72 of 107 (23009)
11-17-2002 5:21 PM


Time for the next installment:
Let's look at Humphreys' equation for "closure interval" which is identical to Wolf's(1998) "equilibrium age."
Tci ~= a^2/(15*D)
As Humphreys defines it, this "closure interval" means the time at which "the loss rate approaches the production rate, an event we call the reopening of the zircon."
This is not strictly correct, and Humphreys admits this is an "estimate" using some simplistic assumptions as a "first approximation." But the equation itself is valid, and Humphreys use of it in this way is off by a factor of only 7.5, so this is not too bad for a Creationist.
If we use this equation to evaluate Humphreys' results, we find some serious discrepancies between reality and Humphreys' ideas.
From Missing Link | Answers in Genesis
...we have this quote:
"After re-opening, [the zircons] would again be an open system, again losing helium as fast as nuclear decay generated it for most of the alleged 1.5 billion years. Today the zircons would have retained less than 0.0002% of the helium, instead of the (up to) 58% observed."
This means the zircons would be unable to accumulate more helium because the "closure interval" was exceeded, diffusion equalling production, after only .0002% of the 1.5 billions year's worth of helium was produced. Thus the "closure interval" in this case is .0002% times 1.5Gya = 3000 years. Remember, this is the way Humphreys uses this equation, so it is not quite right, but even when applying it correctly, the results are the same (in this case).
Thus we have 3000 years ~= a^2/(15*D)
Solving for D/a^2, we get a value for diffusivity of about (7*10^-13)/sec at 378K. (378K = 105degC)
Drawing again from Missing Link | Answers in Genesis ...
Humphreys says:
But the —196C I mentioned in the Impact article is what I will call here the retention temperature. That is the temperature at which the Jemez zircons would have small enough diffusion rates to retain the observed large amounts of helium for 1.5 billion years. That’s essentially what I said in the article:
‘For most of that alleged time [1.5 billion years], the zircons would have to have been as cold as liquid nitrogen (196C below zero) to retain the observed amount of helium.’
That's a very straightforward way of saying the closure interval is long enough to allow the observed level of helium only at the very low temperature of 77K.
If we once more apply Humphreys' "closure interval" equation to approximate the "closure interval" at 77K,
Tci = 1.5Gya = 1/(15*(D/a^2))
...we get a value for diffusivity of (1.4*10^-18)/sec at 77K.
Again, even if we correct Humphreys' usage of this equation, the results are essentially the same (in this case, a little worse for Humphreys).
With 2 values of diffusivity vs temperature, we can now calculate the activation energy and infinite temperature intercept on an Arrhenius plot. I get 2.521 kcal/mol for the activation energy, and (2.0*10^-11)/sec for the infinite temperature intercept.
While Joe and the other geochronologists are cleaning the spittle off their keyboards and monitors, we can use these numbers to illustrate for the rest of us how ridiculous Humphreys' fairy tale has become. If we use the diffusivity constants from above to calculate the closure temperature, we get the astonishing number of 120K !!!
That's minus 153 deg C!!! Yet Humphreys states that he has calcualted a closure temp of +120 to +140 degC for these zircons. So we are right back to where we started. It looks like Humphreys has made some serious mistakes. What they are, we can't tell for sure without seeing all the data that went into his work. But from the results published so far, we can easily see that Humphreys' articles are not even internally consistent.
In the next installment, we will see what realistic values for diffusivity can tell us about these zircons.
.
.
.
.
Refs:
Wolf R.A., Farley K.A. and Kass D.M., 1998. Modeling of the temperature sensitivity of the apatite (U-Th)/He thermochronometer. Chem. Geol., 148: 105-114.
<< edited to correct some minor rounding errors in the math, and a misread digit in one of the ln(D/a^2) results. 2.555 kcal/mol was changed to 2.521 kcal/mol, 2.5*10^-11 was changed to 2.0*10^-11, and (8*10^-13)/sec was changed to (7*10^-13)/sec. The net result was to change the final Tc number from 119K (rounded) to 119.8K (rounded to 120K). In Celsius, it remains at -153C. >>
[This message has been edited by wehappyfew, 11-18-2002]

Tranquility Base
Inactive Member


Message 73 of 107 (23014)
11-17-2002 6:07 PM
Reply to: Message 70 by TrueCreation
11-16-2002 11:40 PM


TB steps forward.

This message is a reply to:
 Message 70 by TrueCreation, posted 11-16-2002 11:40 PM TrueCreation has not replied

wehappyfew
Inactive Member


Message 74 of 107 (23605)
11-21-2002 10:55 PM


Time for another update:
I must say that I am slightly disappointed at the lack of interest or even a response from the YECs on this board and other fora where I have tried to start a discussion of Humphreys' work. Is there something I am not explaining clearly enough, or maybe skipping some crucial concepts needed to understand this material? Or do they just close their eyes to the evidence that one of the most prominent YEC "scientists" has made some serious errors?
Welcome to Chris Ho-Stuart, BTW, we're glad to have you.
I was going to discuss the use of realistic diffusivity constants as measured by Reiners and apply them to Humphreys' zircons. But there's not really much to say. If we use Reiners' experimentally measured values for activation energy and D0 intercept we get the expected closure temp of 190degC; we find that diffusion drops off rapidly at lower temps; and the equilibrium age at 105degC is in the range of hundreds of millions of years or more. No surprises there.
But what I find more interesting is how badly Humphreys' statements and numbers conflict with the physical reality of how diffusion works.
If we examine more closely this paragraph from Humphreys' response to Joe's letter...
"Closure temperature is irrelevant. You misunderstood my statement because you misunderstood closure temperature. You thought that zircons below that temperature would remain a closed system. Wrong! See the preprinted section below to understand why. Even if the Jemez zircons had gone below their closure temperature, according to the uniformitarian scenario they would have re-opened within a few dozen years to a few thousand years after closure. After re-opening, they would again be an open system, again losing helium as fast as nuclear decay generated it for most of the alleged 1.5 billion years. Today the zircons would have retained less than 0.0002% of the helium, instead of the (up to) 58% observed."
In the previous installment (post 72) we've already covered the problems with the 0.0002% number. It requires a diffusion rate that is completely unrealistic given the known diffusivity constants. This time I'd like to point out the sentence in bold above...
"Even if the Jemez zircons had gone below their closure temperature, according to the uniformitarian scenario they would have re-opened within a few dozen years to a few thousand years after closure."
This is not correct. Due to the mathematics of the way closure temperature is calculated, at a temperature just below the closure temp (about 97.5%), the diffusivity (D/a^2) is approximately (1.7*10^-16)/sec. That translates into an equilibrium age of about 1.2 million years, requiring 7.5 times that interval to actually reach the equilibrium. This relationship holds true no matter what the medium, diffusivity constants or closure temp.
For example, if we take the closure temperature calculated by Humphreys (120 to 140 degC), multiply by 97.5% (after converting to Kelvin), we get 110 to 130 degC. At that temp, we calculate the diffusivity (using any combination of diffusivity constants that give the stated closure temp), and find it to be about (1.7*10^-16)/sec. The equilibrium age at that diffusivity is about 1.2 million years. Humphreys cannot have the zircons "re-opening" after a few dozen to a few thousands years when the equilibrium age (he calls it closure interval) is 1.2 million years.
Humphreys' claim in the paragraph cited above is mathematically impossible. All his claims seem to be based on a combination of incorrect data (which we knew right away from the numbers he gave), and now we can add mathematical error to his problems.

wehappyfew
Inactive Member


Message 75 of 107 (25954)
12-08-2002 4:56 PM
Reply to: Message 54 by Tranquility Base
11-10-2002 8:38 PM


quote:
Originally posted by Tranquility Base:
wehappy
It's not that I'm uninterested I just have my doubts whether we'll be able to sort this out from the data we have. So, until its presented somewhere by Humphreys I was perpared to trust. If you can work out what's going on in between then that's great. If you really did present a carefully laid out summary of the ENTIRE story (and calcs you have done) I would be prepared to comment/check. I don't have time to do it completely independently however.
I've laid out several specific problems with Humphreys' paper and response to Meert, including the summary and calculations you asked for.
Are you prepared to comment/check yet?

This message is a reply to:
 Message 54 by Tranquility Base, posted 11-10-2002 8:38 PM Tranquility Base has replied

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